* Astronomy

Title: Ultra Short Period Planets in K2 with companions: a double transiting system for EPIC 220674823
Author: Elisabeth R. Adams, Brian Jackson, Michael Endl, William D. Cochran, Phillip J. MacQueen, Dmitry A. Duev, Rebecca Jensen-Clem, Maïssa Salama, Carl Ziegler, Christoph Baranec, Shrinivas Kulkarni, Nicholas M. Law, Reed Riddle

Two transiting planets have been identified orbiting K2 target EPIC 220674823. One object is an ultra-short-period planet with a period of just 0.57 days (13.7 hours), while the other has a period of 13.3 days. Both planets are small, with the former having a radius of R_p1=1.5 R_E and the latter R_p2=2.5 R_E. Follow-up observations, including radial velocity (with uncertainties of 110 m/s) and high-resolution adaptive optics imagery, show no signs of stellar companions. EPIC 220674823 is the twelfth confirmed or validated planetary system in which an ultra-short-period planet (i.e., having an orbital period less than one day) is accompanied by at least one additional planet, suggesting that such systems may be common and must be accounted for in models for the formation and evolution of such extreme systems.

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